Water-soluble polymers which are prepared by polymerization of ethylenically unsaturated monomers have a wide range of uses as additives in construction chemistry applications and in the development, exploitation and completion of underground mineral oil and natural gas deposits.
U.S. Pat. No. 4,053,323 and U.S. Pat. No. 3,936,408 disclose the use of polyamidosulphonates as flow improvers for hydraulic binders, in particular in the cementing of wells. WO 03/085013 A1 discusses water-soluble copolymers based on olefinic sulphonic acids and the use thereof as fluid loss additives for aqueous building material systems which contain mineral binders. DE 102 29 837 A1 describes polymeric fluid loss additives for drilling fluids and cement slurries based on vinyl-containing sulphonic acids. According to U.S. Pat. No. 4,654,085, polyacrylamide is used together with cellulose ethers and starch ethers as an additive for improving the sag resistance of cement formulations. Furthermore, water-soluble copolymers based on acrylamidoalkylenesulphonic acid, N-vinylamides, acrylamide and vinylphosphonic acid are used for reducing the inflow of water in the extraction of oil or gas (cf. WO 03/033860 A2). EP 0427107 A2 discloses the use of a water-soluble copolymer consisting of ethylenically unsaturated sulphonic acids and acrylamides as a theological additive for drilling fluids. A further field of use for water-soluble polymers which are prepared with the aid of a polymerization of ethylenically unsaturated monomers is the removal of oil from mineral oil-containing sand or rock masses, as discussed in EP 095730 A2. The use of copolymers based on hydrolysed acrylamide and sulphonic acid derivatives as fluid loss additives in cement slurries is described in U.S. Pat. No. 4,015,991.
Fluid loss additives serve for reducing or completely preventing the escape of water from slurries of inorganic or organic binders or pigments. Causes for the water loss are generally capillary forces, which emanate from porous substrata. Fluid loss additives can either bind water to themselves owing to their chemical structure or promote the formation of a dense filter cake on the substratum. Fluid loss additives are used for this purpose, as described above, for example in renders, tile adhesives, grouts, filling and self-leveling materials but also in deep well cement slurries. Moreover, they are used, inter alia, also in aqueous clay suspensions which may serve, for example, as drilling fluids. A number of compounds having such capabilities are known from the prior art. Thus, EP-A 1 090 889 describes mixtures of clay and guar as fluid loss additives. DE-A 195 43 304 and U.S. Pat. No. 5,372,642 disclose cellulose derivatives as fluid loss additives, and EP-A 116 671, EP-A 483 638 and EP-A 653 547 describe synthetic polymers which contain acrylamido-substituted sulphonic acids as comonomers.
All these water-soluble polymers which are known from the prior art and are prepared by polymerization of ethylenically unsaturated monomers are as a rule not biodegradable. Thus, these compounds may accumulate in the environment and contribute to the contamination of soils or bodies of water. This is of particular relevance if cement slurries come into contact, for example, with drinking water or areas used for agriculture. In this context, the use of water-soluble polymers in the exploration and production of mineral oil or natural gas at sea, i.e. in the so-called offshore area, must also be taken into account in particular. Here, these polymers are used, for example, as fluid loss additives for cementitious systems in the construction of drilling platforms and in the cementing of wells. The polymers used may in the first case be washed out by sea water and in the latter case pass over from the cement slurries into water-carrying formation strata. It is for this reason that, according to the “Convention for the protection of the marine environment in the north-east Atlantic” (OSPAR Convention), biodegradable products are to be given preference for use in a marine environment.
In isolated cases, the prior art mentions biodegradable, polymeric additives for cement slurries. Thus, U.S. Pat. No. 6,019,835 discloses modified lignosulphonates as biodegradable flow improvers. The prior published US application 2002/0005287 describes polyaspartic acid as a biodegradable high-performance flow improver. Water-soluble, biodegradable polyamide-based copolymers and the use thereof are disclosed in DE 103 14 354 A1. The copolymers described there have at least one grafted-on side chain, composed of aldehydes and sulphur-containing acids and optionally of at least one compound from the series consisting of ketones, aromatic alcohols, urea derivatives and amino-s-triazines. Natural polyamides, such as caseins, gelatins and collagens, are mentioned as preferred polyamide components. The copolymers described here are used in particular as flow improvers or fluid loss additives for inorganic binders and pigments. The water retention power described is due predominantly to synergistic modes of action of the described copolymers together with modified polysaccharides. it is true that these water-soluble polymers are biodegradable; however, they have as a rule the major disadvantage that they do not permit as large a variability of the chemical composition as the polymers composed of ethylenically unsaturated monomers and are therefore also greatly limited in their range of applications, i.e. for example with respect to temperature or pressure changes or with respect to variations of the aqueous medium in terms of the salt concentration. Since a multiplicity of different ethylenically unsaturated monomers are available, which in each case have different functional groups, a suitable polymer can be “tailored” for many requirements generally by a variation of the monomers.
Gelatin graft polymers are generally disclosed in the European Patent application EP 0 015 880. According to this publication, the polymers are used in receiving elements and serve in particular as dye mordants for photographic materials. The graft polymers described consist at least of three components, which are water-soluble protein-like polymers, a monomer giving a water-insoluble polymer on homopolymerization and finally a monomer containing a sulphonate group and giving a water-soluble polymer on homopolymerization. Gelatin is designated as a typical member of the water-soluble, protein-like polymers and acrylic monomers as typical members of the monomers which give a water-insoluble polymer.
The non-prior-published German document DE 10 2006 038 809.7 discloses a water-soluble and biodegradable polyamide-based copolymer and the use thereof. The copolymer described here contains at least one grafted-on side chain which is composed of ethylenically unsaturated compounds. An additive for compositions containing hydraulic binders and in particular a fluid loss additive are mentioned as a preferred use. The polyamide component is preferably selected from the series of the natural polyamides, degradation products thereof formed by oxidation, hydrolysis or depolymerization, and synthetic polyamides and corresponding degradation products, also being suitable. Typical members of the ethylenically unsaturated component are vinyl-containing compounds. These biodegradable and water-soluble copolymers are also suitable for extreme conditions, as occur in particular in the development, exploitation and completion of underground mineral oil and natural gas deposits and in the case of deep wells. Depending on the composition of the grafted-on side chains, the copolymers described can also be used as flow improvers, it being shown that the flow properties of the slurries to which they have been added significantly improve.
As already discussed, extreme conditions which manifest themselves in particularly high temperatures and salt contents prevail in particular in relation to cementing of wells. Graft polymers of olefinic monomers on brown coal or tannin derivatives as a grafting base are known in this context from the prior art:
U.S. Pat. No. 4,579,927 describes copolymers which are composed of flavanoid tannins and acrylic monomers. Such polymers are water-soluble and show a pronounced thermal stability. Moreover, these copolymers can be used as additives in aqueous drilling fluids. A typical copolymer consists of tannin and ethylenically unsaturated monomers, such as, for example, vinylsulphonic acid. Moreover, substituted amides may also be present. A method for reducing the so-called fluid loss in cementitious compositions which may have high salt concentrations is disclosed in U.S. Pat. No. 4,703,801. The additive described is a graft polymer, whose grafting base may be lignin, lignite or derivatized cellulose. Homopolymers, copolymers and terpolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS), acrylonitrile, N,N-dimethylacrylamide, acrylic acid and N,N-dialkylaminoethyl methacrylate and their salts are suitable as grafted-on groups. Finally, U.S. Pat. No. 4,938,803 describes grafted vinyl lignites which can be used as fluid loss additives. The lignite is grafted with at least one vinyl monomer, it being possible for this monomer also to be present in a mixture with at least one comonomer, such as, for example, AMPS. Finally, reference may be made to the U.S. Pat. No. 5,147,964, according to which vinylically grafted tannins are used for reducing the fluid loss in cement slurries which are employed in the oil field area. In this case, too, AMPS, in addition to acrylamide, is a typical member of the vinyl monomer.
The main disadvantage of all these polymers described in the last-mentioned US documents is their lack of biodegradability, and it is for this reason that they cannot be used in the offshore area, taking into account the application specifications described.